Research will focus on the endocrine control of uterine PGF 2 alpha. Indwelling cannulae will be placed in a utero-ovarian vein, in a deep femoral vein and in a jugular of cows. Blood will be sampled at frequent intervals from day 15 after estrus to day 15 of the next cycle, and ovarian, pituitary and adrenal hormones and PGF2 alpha will be measured to determine the sequence of changes in PGF2 alpha. Similar experiments will be conducted on cows which were inseminated to determine differences in the endocrine controls of PGF2 alpha between pregnant and nonpregnant cows during implantation. On the basis of endocrine corollates with changes in PGF2 alpha, we will design experiments to test directly some potential endocrine controlsof PGF2 alpha. For example, we may administer progesterone alone or sequentially with estradiol to intact and to acutely ovariectomized cows to determine their influence on PGF2 alpha in utero-ovarian venous blood and in uterine endometrium obtained by biopsy. Finally, we will determine PGF2 alpha in utero-ovarian venous blood from cows treated with uterine irritants or oxytocin to cause early luteal regression.